Precision Matthews PM-728VT CNC conversion

Loftfan said:
Hi guys! I've just gotten my 728VT up and running and I'm working out the bugs. It's good to see that my measured backlash is similar to others experience.

After fixing a VERY loud (and jumpy) Z-axis (I had loose phase connections at my Stepperonline CL86T driver), I'm chasing down another issue with the Z-axis.

I seem to be chasing tool offsets, but that would be related to the issue detailed below:

My Z-axis doesn't return to the same position after a move, or several moves over 2 inches (~10 turns of the ballscrew). Moving 0.100" is no issue, it comes right back to the same spot, using a test indicator in a drill chuck. A 2+ inch move won't reliably come back to the same place. It could be 0.010"-0.015" off after a few repetitions, and gets progressively worse with more moves. I'll come back with what I find. Right now, I don't have a clue.
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You are losing steps. I have the same machine and fought the same battle. Hunting down the problem can be frustrating and has a lot of mechanical and electronic variables. My issue was not using rc snubbers on all coils. It has been running great now for 2 years but don't ask me how many times I jogged up and down to figure that one out :eek:
 
GB21 said:
You are losing steps. I have the same machine and fought the same battle. Hunting down the problem can be frustrating and has a lot of mechanical and electronic variables. My issue was not using rc snubbers on all coils. It has been running great now for 2 years but don't ask me how many times I jogged up and down to figure that one out :eek:
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If I am losing steps, the closed loop stepper kits I bought would appear to be useless.

Can you go into more detail on your RC snubber installation?
 
I am using stepper online Y series drives and my mill holds 0.001 all day. I went with these drives because the accept 24v and I am using centroid acorn and didn't want to drop to 5v signal but CL86T and CL86Y are pretty much the same. Snubbers or quencharc's are likely not your problem yet if your just jogging around. They are necessary on anything that has a coil such as vacuums and solenoids for example I use pneumatic solenoid valves for mist coolant, ATC and my 4th axis. I use cheap ones like these https://www.amazon.com/gp/product/B09F116Y27/ref=ppx_yo_dt_b_asin_title_o08_s00?ie=UTF8&psc=1

I don't know what controller you are using but keep in mind they claim a max input of 200kHZ frequency but these drives are not fast enough as verified by a oscilloscope( that took me another year to figure out) . I set mine to 100kHZ

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GB21 said:
I am using stepper online Y series drives and my mill holds 0.001 all day. I went with these drives because the accept 24v and I am using centroid acorn and didn't want to drop to 5v signal but CL86T and CL86Y are pretty much the same. Snubbers or quencharc's are likely not your problem yet if your just jogging around. They are necessary on anything that has a coil such as vacuums and solenoids for example I use pneumatic solenoid valves for mist coolant, ATC and my 4th axis. I use cheap ones like these https://www.amazon.com/gp/product/B09F116Y27/ref=ppx_yo_dt_b_asin_title_o08_s00?ie=UTF8&psc=1

I don't know what controller you are using but keep in mind they claim a max input of 200kHZ frequency but these drives are not fast enough as verified by a oscilloscope( that took me another year to figure out) . I set mine to 100kHZ

​

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Thanks for the tips, I'll be adding a coolant solenoid soon.

I'm also using Centroid Acorn. I'll make the adjustment you did.
 
I found a very likely cause for my issue of the Z-axis drifting downward. I locked the gib on the head slide and actuated the Z-axis. What I saw surprised me (see video in link)!


After this video, I tightened the locknut and actuated the axis a few more times until I had 0.015" of drift. Tightening the nut again brought the head position back to where it started.

I bought the "precision" ballscrew kit from Precision Matthews

When I was tightening the ballscrew locknuts, I never did get a good bite on the setscrews. Apparently, my Z-axis locknut has been backing out for a while now. I suspect that my small allen wrenches are worn out, because none of them fit this tiny 2mm setscrew well. I bought a new set of wrenches yesterday and I'll try to get it locked down. I checked the X-axis, and it was loose too. I bet the Y is the same case.

What is the torque spec on the ballscrew locknuts? There wasn't any guidance in the kit. These locknuts are grooved to accept a small hooked spanner wrench. I'll see if I can buy a torque adapter for my torque wrench. I'm guessing the torque spec is somewhere in the in-lb scale.
 
Loftfan said:
I found a very likely cause for my issue of the Z-axis drifting downward. I locked the gib on the head slide and actuated the Z-axis. What I saw surprised me (see video in link)!


After this video, I tightened the locknut and actuated the axis a few more times until I had 0.015" of drift. Tightening the nut again brought the head position back to where it started.

I bought the "precision" ballscrew kit from Precision Matthews

When I was tightening the ballscrew locknuts, I never did get a good bite on the setscrews. Apparently, my Z-axis locknut has been backing out for a while now. I suspect that my small allen wrenches are worn out, because none of them fit this tiny 2mm setscrew well. I bought a new set of wrenches yesterday and I'll try to get it locked down. I checked the X-axis, and it was loose too. I bet the Y is the same case.

What is the torque spec on the ballscrew locknuts? There wasn't any guidance in the kit. These locknuts are grooved to accept a small hooked spanner wrench. I'll see if I can buy a torque adapter for my torque wrench. I'm guessing the torque spec is somewhere in the in-lb scale.
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Those tiny setscrews are worthless. Mine kept coming loose on the z and y also. I used jam nuts and tightened them against the locknut with a drop of threadlocker. problem solved. You should start your own build thread so we can follow along.

 
GB21 said:
Those tiny setscrews are worthless. Mine kept coming loose on the z and y also. I used jam nuts and tightened them against the locknut with a drop of threadlocker. problem solved. You should start your own build thread so we can follow along.

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Many thanks for your guidance on adding the locknuts. After this was fixed, I burnt up my Stepperonline CL86T Z-axis driver (don't control the v3 version with 24v. They need an in-line resistor!). Once that was replaced, I'm repeatable within a thousandth!

My homemade Fogbuster is working great, too. I have the four-way hose fittings (which were the only parts not available on the market) for the water filter housing for sale on Etsy - Click Link Here.
 

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Loftfan said:
Many thanks for your guidance on adding the locknuts. After this was fixed, I burnt up my Stepperonline CL86T Z-axis driver (don't control the v3 version with 24v. They need an in-line resistor!). Once that was replaced, I'm repeatable within a thousandth!
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Wait - what about the CL86T needing a in-line resistor???? Where can I find more information before I power mine up?
 
cxagent said:
Wait - what about the CL86T needing a in-line resistor???? Where can I find more information before I power mine up?
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Link to v3.0 Manual

If you have a v3.0 controller WHICH IS STILL BEING SHIPPED TWO YEARS AFTER V4.0 WAS INTRODUCED, look at pg7 in the manual. There, the resistor values are given. My controller uses 24v, and my CL57T's contained a switch to select between 24v control and 5v control. I assumed the CL86T was the same version, but it wasn't. I burnt a tiny 250ohm resistor on the circuit board for the direction circuit.

I have 2kOhm resistors in line now. My replacement driver was another CL86T v3.0 :oops:
 
As my system has been up about a year, it's time to clean it, lubricate, tighten, and just give it a general go-over.

I just had my x-axis double nut repacked and tightened by Dave who makes the Arizona CNC kits. As many others can testify, Dave is very knowledgeable and a nice guy to talk to. I am also lucky that he lives in the Phoenix metro area and he welcomed me in his shop. I am going to post some updates on the machine's performance.
 
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